docs: def add_options(self):
          """ Add program options.
          """
          super(ThemeSwitcher, self).add_options()
  
          self.add_bool_option("-l", "--list",
              help="list available themes")
          self.add_bool_option("-c", "--current",
              help="print path to currently selected theme")
          self.add_bool_option("-n", "--next",
              help="rotate through selected themes, and print new path")
          self.add_bool_option("-a", "--all",
              help="remove any selections, and use all themes")
          self.add_value_option("-t", "--toggle", "NAME",
              help="toggle selection of a theme")